它被称为抽象类，用于实现虚函数.它适用于四个类似实现中的三个
It is said abstract class for a virtual function that is implemented. It works with three of four similar implementations
这似乎只是circle.cpp的问题，即使代码在point.cpp中看起来相同。我一直在看代码很长一段时间了，我没有发现这两个文件有什么不同。下面是错误信息:
>------ Build started: Project: ou5, Configuration: Release Win32 ------
1> circle.cpp
1> ou5.cpp
1>c:usersjonasdocumentsvisual studio 2010projectsou5ou5shapeptr.h(52): error C2259: 'Shape' : cannot instantiate abstract class
1> due to following members:
1> 'Shape *Shape::clone(void) const' : is abstract
1> c:usersjonasdocumentsvisual studio 2010projectsou5ou5shape.h(21) : see declaration of 'Shape::clone'
1>ou5.cpp(20): error C2259: 'Shape' : cannot instantiate abstract class
1> due to following members:
1> 'Shape *Shape::clone(void) const' : is abstract
1> c:usersjonasdocumentsvisual studio 2010projectsou5ou5shape.h(21) : see declaration of 'Shape::clone'
1>ou5.cpp(27): error C2259: 'Shape' : cannot instantiate abstract class
1> due to following members:
1> 'Shape *Shape::clone(void) const' : is abstract
1> c:usersjonasdocumentsvisual studio 2010projectsou5ou5shape.h(21) : see declaration of 'Shape::clone'
1> point.cpp
1> polygon.cpp
1> rectangle.cpp
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
带有纯虚函数的基类代码:
#ifndef SHAPE_H
#define SHAPE_H
using namespace std;
#include <iostream>
#include <ostream>
class Shape
{
public:
Shape()
{
cout << "Shape constructor" << endl;
}
Shape(double xval, double yval)
{
x = xval;
y = yval;
}
virtual Shape* clone() const = 0;
virtual double area()
{
return 1;
}
virtual void print() const{}
virtual ostream& printf(ostream &os){return os;}
/* // Copy constructor
Shape(const Shape *sp)
{
// Copy the string into our newly allocated memory
sp =this->clone();
}*/
/*Shape & operator=(const Shape & sptr)
{
if(this!= &sptr)
{
*this = sptr.clone();
}
return *this;
}*/
double getx() const
{
return x;
}
double gety() const
{
return y;
}
virtual ~Shape() {cout << "Shape raderas av destruktor" <<endl; }
protected:
double x; //Attribut
double y; //Attribut
Shape *sp;
};
#endif
正在工作的点h:
#ifndef POINT_H
#define POINT_H
#include "shape.h"
using namespace std;
#include <iostream>
#include <fstream>
class Point : public Shape
{
public:
Point()
{
cout << "Point constructor" << endl;
}
Point(double x, double y, double sz) : Shape(x,y), size(sz)
{
cout << "Point constructor" << endl;
}
void las(istream &is)
{
is >> x >> y >> size;
}
ostream& printf(ostream &os) ;
void print() const;
double area();
Shape* clone() const;
virtual ~Point(){cout << "Point raderas av destruktor" << endl;}
private:
double size; //Attribut
};
#endif
point.cpp:
#include "point.h"
#include <ostream>
using namespace std;
Shape* Point::clone() const { return new Point( *this); }
void Point::print() const
{
cout << "POINT: ";
cout <<"(" << this->x<<"," << this->y << ")" << this->size << endl;
}
ostream& Point::printf(ostream &os)
{
os << "POINT: ";
os <<"(" << this->x<<"," << this->y << ")" << this->size << endl;
return os;
}
double Point::area()
{
return size;
}
有问题的文件。第一个circle.h:
#ifndef CIRCLE_H
#define CIRCLE_H
#include "shape.h"
using namespace std;
#define M_PI 3.141592654
#include <fstream>
#include <iostream>
class Circle : public Shape
{
public:
Circle()
{
cout << "Circle constructor" << endl;
}
Circle(double x, double y, double rad) : Shape(x,y), radie(rad)
{
cout << "Circle constructor" << endl;
}
void las(istream &is)
{
is >> x >> y >> radie;
}
ostream& printf(ostream &os);
double area();
void print() const;
Shape* clone() const;
virtual ~Circle(){cout << "Circle raderas av destruktor" << endl;}
private:
double radie; //Attribut
};
#endif
然后circle.cpp:
#include "circle.h"
using namespace std;
#include <ostream>
Shape* Circle::clone() const {return new Circle( *this);}
double Circle::area()
{
double tmparea;
tmparea = M_PI * radie * radie;
return tmparea;
}
void Circle::print() const
{
cout << "CIRCLE: ";
cout <<"(" << this->x<<"," << this->y << ")" << this->radie << endl;
}
ostream& Circle::printf(ostream &os)
{
os << "CIRCLE: ";
os <<"(" << this->x<<"," << this->y << ")" << this->radie << endl;
return os;
}
问题是clone，它在文件工作和不工作的文件中看起来是一样的。工作文件是point.cpp，但它也可以与其他两个文件一起工作。
我在这里添加了shapeptr.h:
#ifndef SHAPEPTR_H
#define SHAPEPTR_H
#include "shape.h"
#include "circle.h"
#include "point.h"
#include "polygon.h"
#include "rectangle.h"
#include <ostream>
#include <istream>
#include <vector>
#include <fstream>
#include <string>
using namespace std;
class ShapePtr
{
public:
ShapePtr()
{
sptr = 0;
numshapes = numshapes + 1;
}
ShapePtr(Shape * v)//: Shape(v->getx(),v->gety())
{
sptr = v;
numshapes = numshapes + 1;
}
// Copy constructor
ShapePtr(const Shape &sp)
{
// Copy the string into our newly allocated memory
sptr = sp.clone();
}
const ShapePtr & ShapePtr::operator=(const Shape & sp)
{
if(this->sptr!= &sp)
{
sptr = sp.clone();
}
return *this;
}
~ShapePtr(){
numshapes = numshapes - 1;
cout << "ShapePtr raderas av destruktor" << endl;
}
Shape getshape()
{
return *sptr;
}
private:
Shape *sptr;
public:
static int numshapes;
friend istream& operator>>(istream &is, ShapePtr & sp);
friend ostream& operator<<(ostream &os, const ShapePtr & sp);
};
int ShapePtr::numshapes = 0;
ostream& operator<<(ostream &os, const ShapePtr & sp)
{
os << sp.sptr->printf(os);
return os;
}
istream& operator>>(istream &is, ShapePtr & sp)
{
string check;
while(!is.eof())
{
is >> check;
if(check == "Circle")
{
Circle cir;
cir.las( is );
sp = ShapePtr(new Circle(cir));
return is;
}
if(check == "Polygon")
{
Polygon pol;
pol.las( is );
sp = ShapePtr(new Polygon(pol));
return is;
}
if(check == "Point")
{
Point poi;
poi.las( is );
sp = ShapePtr(new Point(poi));
return is;
}
if(check == "Rectangle")
{
Rectangle rec;
rec.las( is );
sp = ShapePtr(new Rectangle(rec));
return is;
}
}
}
#endif
根据您的评论，您正试图在Shapeptr.h中创建一个无效的abstract class实例。您尝试创建这个实例的位置在这里:
Shape getshape()
{
return *sptr;
}
正如Mark b指出的那样，修复方法是将返回类型更改为Shape&。
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- 它被称为抽象类，用于实现虚函数.它适用于四个类似实现中的三个
